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I tried with two different gas regimes: CF4 and C4F8. I only made a few tests with CF4 since I got a very bad selectivity to the resist mask and I dicided to go for the C4F8 instead.

C4F8

I started out with a recipe developed by Peixiong called pxSiO2try9, look at his results here

Parameter	Mask material	Barc etch	Coil power	Platen power	Pressure	Flow rate C4F8	Flow rate H2	Flow rate Ar	Process time	Comment	CD change (mask 55% trench) after s007467 is it <50% after barc etch trench opening as a fraction of pitch	Profile angles	Etch depth in SiO2	Etch rate	Etch depth in resist	Selectivity (resist:SiO2)	Etch rate in Si
s008684	880nm KRF	barc etch CF 50s	1000W	200W	2.5mTorr	13sccm	30sccm	0	1:30min	The layer in this case is 300nm Si3N4	35% (1µm pitch) 47% (6µm pitch)	83-88		>300nm/min (Si3N4)	240nm	~1:2 (Si3N4)	?
s006656	750nm KRF	none	1000W	150W	2.5mTorr	15sccm	0sccm	30sccm	10min	Tried with C4F8/Ar instead of C4F8/H2 => much lower etch rate and bad selectivity to the resist.			358 nm	35.8 nm/min (2µm pitch)	526nm	1:0:68
s006106	750nm KRF	Barc etch O2 75s	800W	150W	2.5mTorr	8sccm	30sccm	0	10min	From Peixiong	60%	79	1053 nm (center) 1043 nm (edge)	105 nm/min	280nm	1:3:75 (2µm pitch)

CF4

I stopped trying with CF4 because I got bad selectivty to the resist and decided to focus on the recipe with C4F8 instead.

Parameter/Wafer ID	s006687	s006701	s007258	s007350	s007352
Mask material	750nm KRF	750nm KRF	750nm KRF	750 nm KRF	750nm KRF
Barc etch	none	none	none	none	none
Coil power	800W	800W	800w	800w	800w
Platen power	100W	100W	100w	60W	30w
Pressure	4mTorr	4mTorr	4mTorr	4mTorr	4mTorr
Flow rate CF4	20sccm	25sccm	30sccm	30sccm	30sccm
Flow rate H2	20sccm	15sccm	10sccm	10sccm	10sccm
T	0	0	0	0	0
Process time	10min	10min	2min30	2min30	3min30
Comment			Little resist left, Trenching	A little trenching	very little trenching in large lines - anti trenching in small lines
Results	profile near edge Profile near middel	tilted profile	s007350 2µm pitch	s007350 2µm pitch s007350 1µm pitch	s007352 1µm pitch s007352 2µm pitch
Etch depth in SiO2	374nm	505nm	578nm	336nm	235nm
Etch rate	37.4nm/min	50.5nm/min	231nm/min	134.4nm/min	88nm/min
Etch depth in resist	345nm	633nm	700nm	405nm	308nm
Selectivity (resist:SiO2)	1:1.1	1:0.80	1:0.83	1:0.83	1:0.76